Electron impact excitation the lower levels of Mg, Ca and Sr atoms


Background. Progress in the field of physics of electron-atom collisions is dependent on two main factors: a) the availability of new studies of individual atomic systems; b) the clarify, systematize and generalize of results, obtained in previous studies. In the last decade we, together with co-authors, investigate in detail the elastic and inelastic electron scattering on neutral atomic systems Ca, Mg, Sr, Si, F, Al, and B. The purpose of this paper is to systematize and summarize the results of studies of alkaline-earth atoms Ca, Mg and Sr, for the possibility of using established patterns in the calculation of new atomic facilities.
Methods. The atomic structures for Mg, Ca and Sr, as well as the excitation cross sections for e−Mg, e−Ca and e−Sr scattering processes were obtained by the B-spline R-matrix method. The multiconfiguration Hartree-Fock method with nonorthogonal orbital sets was employed for an accurate representation of the targets wave functions. The close coupling expansions include 37 spectroscopic states of neutral magnesium, 39 states of calcium and 31 states of strontium, respectively. The scattering calculations was then carried out in the same way as in standard R-matrix calculations.
Results. In this paper we summarize our earlier data with electron-atom scattering on Mg, Ca and Sr. The subject of the study are energy and angular dependences of integral (ICS) and differential (DCS) cross sections of electron impact excitation of the lower levels of these atoms. We reviewed the transitions from the ground state ns2 1S (n = 3, 4, 5 for Mg, Ca and Sr, respectively) in the nsnp 1,3Po, ns(n−1)d 1,3D [or 3s3d 1,3D for Mg], ns(n+1)s 1,3S and ns(n+1)p 1,3Po states.
Conclusions. We have shown, that the form of the energy dependence of the electron-impact excitation cross sections for Mg, Ca and Sr atoms, are determined by the type of spectroscopic transition between the initial and final states of the target atom, as well as by the general placement of the energy levels of the their excited states. An analysis of the angular and energy dependences behaviour of the excitation DCSs for these atoms confirms this conclusion

Keywords: Mg, Ca and Sr atoms, electrons scattering, B-splines R-matrix method, integral and differential excitation cross sections